1. Field of the Invention
The present invention relates to an address resolution method and an address resolution communication system for a mobile packet terminal in a mobile communication system serving as a connection oriented type network, and more particularly to an address resolution method and an address resolution communication system for a mobile terminal which is changed at any time by handover of the mobile terminal when the mobile packet terminal and a connectionless type network are connected to each other.
2. Description of the Related Art
An address resolution protocol ARP is a protocol for dynamically associating an IP address and a physical address (MAC address in the case of Ethernet) in the Internet protocol IP. For example, when the physical address (00-22 bit-24 bit) of a target host is not known although the IP address (123, 45, 67, 8) thereof is known, an IP packet containing a destination IP address as “address resolution request” is transmitted to all the terminals in order to known the physical address of the target host. When a terminal receiving the IP packet checks the IP address and knows that it is a request addressed to the terminal itself, the terminal returns its own physical address as “address resolution reply”. Here, when the “address resolution request” is transmitted via a switch node (SW), an address management table of the switch node (SW) stores an IP address and a physical address passed through each input/output port to store the terminal connected to the tip of each input/output port.
The “address resolution reply” returned from the destination terminal arrives at the transmission origin terminal to allow the transmission source terminal to refer to the physical address of the destination terminal. Therefore, the transmission source terminal can create a frame in which the physical address of the communication partner host is set, and transmit the IP packet to the connectionless type network.
Here, an “address resolution request” packet in which the destination IP address and the transmission source address are set to the same address is referred to as “Gratuitous-ARP” of the present invention as described later. A terminal transmitting this ARP packet does not expect any reply. A terminal which receives the Gratuitous-ARP packet discards it if the IP address thereof is not the IP address of the terminal itself. On the other hand, if the IP address is the IP address of the terminal itself, the terminal returns a reply. Therefore, both the transmission terminal/reception terminal can detect the duplication of the IP address.
The above operation is associated with the address resolution system. However, for the communication system based on the mobile packet terminal in which the terminal moves, a mechanism of performing address resolution has been proposed as the 2002nd of the RFC (Request For Comment) document (see RFC2002). The detailed description on the Mechanism of Mobile IP is omitted because it is based on the “RFC2002” document.
As described above, when the packet terminal is fixed, in the network containing the switch node, the association between the respective input/output ports of the terminal and the switch node is not changed. However, when a terminal having a radio line is used as a physical layer protocol, there occurs so-called “handover” in which the mobile packet terminal moves to a different place. In this case, a node and an inter-working device (IWF) which terminate the radio line are physically changed.
As the radio line has been known an IS-95 system which is standardized in EIA (Electronic Industries Association), TIA (Telecommunication Industry Association), ANSI (American National Standard Institute) and CDG (CDMA Development Group) serving as institutes of standards of U.S.A. The IS-95 system is supplied as a public mobile communication system using techniques such as double code arrangement and soft handover, and a spread spectrum technique. The inter-working device (IWF: Inter-Working Function) is defined as a device having an interfacial function as a mutual connection unit for performing mutual connections between the connection oriented type communication system and the connectionless type communication system.
FIG. 1 shows the operation of the handover in a network having a switch node. As shown in FIG. 1, the radio-communication system comprises a mobile packet terminal (MS1:Mobile Station 1A), base station radio devices (BTS2: Base transceiver stations 1A, 2B), base station controllers (BSC3: Base Station Controllers 3A, 3B), a mobile communication switching station (MSC4: Mobile Switching Center 4), a switch node 6, a packet network 7 connected to the outside and an inter-working device (IWF) 5 for connecting a radio interface an a packet network.
FIGS. 7 and 8 show data transmission on the basis of a conventional address table.
A mobile station MS1A is connected to a base transceiver station (BTS2A) (not shown) through a radio line, and also connected through a base station controller (BSC3A) to an inter-working function locating in the range and a port 61 of the switch node 6. The switch node 6 has plural ports for the mobile stations such as a port 62 for the base station controller (BSC3B) (not shown), etc., a port 63 to be connected to the packet network serving as the connectionless type network, a switch port 65 as a transfer change-over switch and an address management table 64.
The address management table 64 has a corresponding table which associates the physical address of a mobile station (MS) 1A (for example, a mobile device ID) with a port (for example, port 61) on the basis of an “address resolution request” transmitted from the mobile station (MS) 1A.
When the mobile station MS1A transmits an IP packet containing a destination address and a transmission source address, the IP packet is transmitted through BTS2A, BSC3A, the inter-working function (IWF) 5A and the port 61 to a switch portion 65.
The switch portion 65 refers to the address management table 64 on the basis of the destination address of the IP packet to determine the physical address of the packet network 7, and outputs the IP packet to a port 63 directing to the packet network 7. Conversely, when a call is made to the mobile station MS1A, the port 61 at which the physical address of the mobile station MS1A is registered is likewise determined on the basis of the address management table, and the IP packet is transmitted to the mobile station MS1A serving as a destination.
As described above, when an inter-working function (IWF) for connecting a radio line serving as a connection oriented type network and a connectionless type network is changed like the inter-working function (IWF) of the range in which the mobile station MS1A locates is handed over to a different inter-working function (IWF) 5B, the input/output ports of the switch node provided to the connectionless type network are changed. In this case, the port 61 registered in the address management table 64 is inconsistent with the physical address of the actual MS1A, and thus there occurs unconformity between the IP packet transmitted to each input/output port and the physical address management table provided to the switch node.
Therefore, it is impossible that the IP packet addressed to MS1A is transmitted to the inter-working device IWF5A.
As described above, when the mobile station MS1A is handed over, it is necessary to promote the switch node to change the association of the logical-physical addresses. However, in the prior art, the functions must be installed in cooperation between the packet network and the mobile station by using the Mobile IP serving as the mobile management protocol, and thus compatibility and processing capability of nodes are required.